Among steering apparatuses commonly used in mid to small vessels such as motorboats and pleasure boats, there are such apparatuses that transmit the operating motions of the steering wheel via steering cable such as wire to the rudder.
FIG. 9 shows a typical example of steering apparatus of the prior art which employs the steering cable.
A vessel 1 is provided with a steering wheel 2 for maneuvering the vessel. A rudder 3 is provided at the stern apart from the steering wheel 2. The steering wheel 2 and the rudder 3 are connected with a transmission line 4 consisting of a steering cable.
The rudder 3 in this case is constituted from an outboard engine which consists of an engine 3a and a screw 3b. 
When an operator operates the steering wheel 2, the transmission line 4 is drawn out or drawn in, so as to move back or forth. The transmission line 4 is connected to a rod 6 of a guide 5 so that the rod 6 moves back and forth as the transmission line 4 moves back and forth. As the rod 6 move back or forth, a lever 8 is moved via a connecting rod 7 to the left or right, so as to change the direction of the rudder 3 (outboard engine).
Such a method of steering that transmits the control quantity due to the operation of the steering wheel 2 in the form of reciprocal motion of the transmission line 4 such as steering cable to the rudder 3, as described above, has an advantage of building the apparatus very easily at a low cost. Also because it enables it to make the transmission line 4 from a flexible material such as the steering cable, the line can be installed with a higher degree of freedom. Thus the line can be routed around other units so as to avoid interference therewith.
However, since a manual steering apparatus that employs the steering cable as described above requires it to steer the rudder 4 by operating the steering wheel 2 only by the power of a human operator, there has been such a problem that it is not convenient for a weak-powered operator such as female.
Also because it requires a considerable manual force to steer, larger vessels are difficult to steer with human power. As a result, sizes of the applicable vessels are limited within certain level and the apparatus cannot be applied to larger vessels.
An object of the present invention is to provide a steering apparatus which eliminates the drawbacks of the conventional steering apparatuses and allows it to steer with a reduced force without requiring the operator to exert a strenuous effort while maintaining the advantages of the steering apparatus that employs the steering cable such as simple constitution, low cost and ease of installation.
It is another object of the present invention to provide a steering apparatus which can be applied to larger vessels than the vessels equipped with the conventional steering apparatuses employing the steering cable.
Further another object of the present invention is to provide a steering apparatus which gives the operator the real feeling of manual steering.
It is of course included in the objects of the present invention to provide a steering apparatus which ensures sufficient safety such that the rudder will never be steered only by assisting force supplying means without the operator actually operating the steering apparatus.